tell if child window is open in code behind parent window-web app

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Hi just wondering if anyone knows if there is a way to tell if a child window
is still open in the code behind in the parent window (web application vs.net
2005)? I have a web app and am using the following to add an attribute to
the body tag,
body.Attributes .Add("onunload" ,
"opener.locatio n.href=opener.l ocation.href;") ;. This causes the parent page
to reload anytime the child page has a post back event or closes. Also I am
getting an error when trying to grab data in the parent page from the child
page (saved in session variable). The error is (unnable to cast object to
type system.collecti ons.generic.lis t'[parent page]to
System.collecti ons.generic.lis t[child page]). This error is occuring on the
parent page, line
linksDataReposi tory = (List<structRep o>)Session["linksDataRepos itory"];
where List<structRepo linksDataReposi tory;//generic list of type structRepo
and for structRepo which is just a structure I have
public struct structRepo
{
public Int32 icount;
public String url;
public String abspath;
public String description;
}
I have structRepo and linksDataReposi tory defined the same on both the child
and parent page. The linksDataReposi tory list is filled and saved to a
session variable in the child page.

Thanks
Paul G
Software engineer.